<div class="row form-group">
  <div class="col-sm-6">
    <label class="col-sm-3 control-label">Código AFIP</label>
    <div class="col-sm-6">
     <input type='text' class='form-control' name='f_txt_codigo' placeholder='Código'>
    </div>
  </div>

  <div class="col-sm-6">
    <label class="col-sm-3 control-label">Descripción</label>
    <div class="col-sm-6">
      <input type='text' class='form-control' name='f_txt_descripcion' placeholder='Descripción'>
    </div>
  </div>
</div>